Agricultural products, such as vegetables and flowers, are grown on a large scale in greenhouses throughout the world. During daylight hours, growing agricultural products introduce water vapor into the greenhouse and extract carbon dioxide from the air. The growth of such products is enhanced when excess carbon dioxide is introduced into the greenhouse during daylight hours. This can be accomplished, particularly if heat is needed during the day, by burning LP or natural gas and passing the products of combustion directly into the greenhouse. Water heated by burning the fuel can be stored during the day to provide a reservoir of heat that can be released during the night time to heat the greenhouse. The primary deficiency of this approach is the water vapor contained in the flue gases. When this water vapor is added to the water vapor produced by the the growing agricultural products, saturated or nearly saturated conditions are created within the greenhouse. This condition of high humidity produces undesirable stress on all but tropical plants, and increases susceptibility the plants to various diseases which require periodic spraying or other treatment. As a consequence, considerable resistance thas been encountered in applying this approach to greenhouse management.
It is therefore an object of the present invention to provide a new and improved method of and apparatus for controlling the condition of air in an enclosure such as a greenhouse, where the disadvantages of the prior art are substantially overcome or reduced.